I never did Alien before going to see ALIENS, I think the main reason for that was that a) I don’t like horror films and b) I was too young to get into the cinema when it came out.
ALIENS is in many ways a very different film to the original Alien, I sometimes think they are two very different films which just so happen to be linked.
As for the next two sequels, well I was very disappointed. I think I would have rather seen a sequel with the Colonial Marines rather than the Alien and Ripley. I have seen Prometheus and I did think that this was a very good film.
The main thrust of ALIENS is that is a action war film, rather than the claustrophobic individual horror that was Alien. The design echoed current military thinking of the time, so was more “realistic” than say Starship Troopers.